IN architectures are based on limiting the function of switches in a switch-based network (e.g., a PSTN) to basic circuit management/call control and moving all value-added services for a call to processors outside of the switch network. This structure provides the network operator with the means to develop and control value-added call services more efficiently, instead of relying on switching system vendors for software development. New capabilities can be rapidly introduced into the network, and, once introduced, services are easily customized to meet individual customer's needs.
A typical IN architecture distributes service logic, data and service assistance functions throughout the telecommunications network. IN networks provide enhanced call services such as voice mail, single number reach, speech recognition, call screening and the like.
In the typical IN architecture, a call is routed to a service switching point (SSP) from a switching system as a result of the activation of a trigger (for example, the dialed directory number, call forward on busy, or the like). The control information for the call is sent to the SSP's control computer which determines the service to be performed and instructs the switch fabric of the SSP to sequentially connect the call to one or more service circuits (each known as a service control point (SCP)) as appropriate for the applicable service. The connection between the SSP and SCP is typically on a Signaling System 7 (SS7) network, in accordance with established communication protocols therefor.
In return, each SCP instructs the SSP about providing the required service to the call.